module type S_invertible = Piecewise_linear_intf.S_invertible
include Piecewise_linear_intf.S
create
enforces that the x (key) values are strictly increasing. It also enforces
that the y (value) values are either strictly increasing or strictly
decreasing. These two properties give us invertibility.val get_inverse : t -> value -> key
get_inverse t value
is the inverse operation of get t key
.